feat: add limit-req demo

[spacewander]

Please answer these questions before submitting a pull request

1. Related issues (for new feature or improvement, one should submit an issue first before writing code): Fix #12

[codecov-commenter]

Codecov Report

Merging #16 (501782d) into master (82c36f2) will decrease coverage by 0.03%. The diff coverage is 77.77%.

:exclamation: Current head 501782d differs from pull request most recent head 02519f8. Consider uploading reports for the commit 02519f8 to get more accurate results

@@            Coverage Diff             @@
##           master      #16      +/-   ##
==========================================
- Coverage   78.85%   78.81%   -0.04%     
==========================================
  Files           9       10       +1     
  Lines         487      505      +18     
==========================================
+ Hits          384      398      +14     
- Misses         82       84       +2     
- Partials       21       23       +2     

Impacted Files	Coverage Δ
cmd/go-runner/plugins/limit_req.go	77.77% <77.77%> (ø)

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[spacewander]

Will add it later.